Zdeněk Tuzar

The structure of low conversion polymers of ethylene dimethacrylate

Abstract Results of study of the pregel chain polymerization of ethylene dimethacrylate in the presence of various amounts of diluent suggest the formation of compact microgel-like particles even at the very beginning of polymerization, as a consequence of predominant cyclization. This view is based on following experimental findings. The fraction of units with pendant vinyls (70 mol %) is independent of conversion and depends only slightly on dilution; critical conversion at gelation is displaced by a factor of about 10 2 ; molecular weights at the beginning correspond approximately to molecular weights of poly(methyl methacrylate) obtained under the same conditions; intrinsic viscosities are very low and much lower than those of strongly branched poly(methyl methacrylates).

Dilute and semidilute solutions of ABA block copolymer in solvents selective for A or B blocks: 2. Light scattering and sedimentation study

Abstract Micellar solutions of a triblock copolymer polystyrene- block -poly(hydrogenated butadiene)- block -polystyrene, in heptane and in 1,4- dioxane 25 vol % heptane have been studied by light scattering and sedimentation velocity methods. In dilute solutions, micellar molar mass, hydrodynamic radius of micelles, average volume fraction of polymer segments in a micellar core and in the whole micelle, and the unimer/micelles ratio have been determined. While in semidilute mixed solvent solutions only one diffusion mode, corresponding to collective diffusion, has been determined, at least two modes, diffusion and relaxation ones, have been observed in spectra of decay times in semidilute heptane solutions. Micellar models have been proposed for both systems under study, accommodating satisfactorily all experimental results.

Small-Angle Neutron Scattering Study of Onion-Type Micelles

Onion-type block copolymer micelles were prepared drom polystrene-block-poly(2-vinylpridine) (PS-b-PVP) inner micelles in an acidic solution by basyfyting in the presence of polystrene-block-poly(2-vinylpridine)-block-poly(ethylene oxide) (PVP-b-PEO). This has the effect of depositing the PVP-b-PEO onto the collapsed corona of the PS-b-PVP micelle. These core PS-b-PVP micelle, the small micelles formed by PVP-b-PEO, and the resulting onions micelles were studied by small angle neutron scattering (SANS) techniques . Two recently developed evaluation techniques were employed: 1.Bare-core approximation, which utilizes the data at larger scattering anles provided information about the size and polydispersity of the micelle core. 2. Application of the Pedersen and Gerstenberg micelle model, which utilizes the whole scattering curve. Due to their polyelectrolyte nature, the core micelles had very extentde coronas corresponding to rather large stastistical segment lengths. The SANS data at large scattering angles for the solution of onions-type micelles revealed the presence of a significant number of the small PVP-b-PEO micelles. The contribution of the small micelles to the total scattering was subtracted and the properties and polydispersities of onions cores and stabilizing PEO coronas were obtained.

Dilute and semidilute solutions of ABA block copolymer in solvents selective for A or B blocks: 1. Small-angle X-ray scattering study

Abstract Solutions of a triblock copolymer, polystyrene- block -poly(hydrogenated butadiene)- block -polystyrene, in a selective solvent either for the aliphatic middle block (heptane) or for the polystyrene outer blocks (1,4-dioxane/25 vol% heptane) were studied by viscometry and small-angle X-ray scattering. In both systems, micelles were detected with uniform spherical cores formed by insoluble copolymer blocks. In semidilute solutions, in concentration regions above 0.01 g cm −3 in heptane and ∼0.1 g cm −3 in the mixed solvent, micelles were found to be space-correlated, the effect being accompanied by a steep increase in zero-shear viscosity. Aliphatic micellar cores in the mixed solvent are highly swollen due to the effect of selective sorption.

Formation of block copolymer micelles: a sedimentation study

Abstract The formation of block copolymer mixed micelles has been studied in solutions of polystyrene-block-polyisoprene and polystyrene-block-poly(ethylene-co-propylene) in decane, a selectively poor solvent for polystyrene blocks. The rate of mass exchange between two types of micelles, studied by the sedimentation velocity method, depends strongly on the rates of micelle formation and dissociation processes, which can be controlled by temperature.

The glucan-chitin complex in Saccharomyces cerevisiae

Scar rings (SR) from scarless cells at the early stages of budding and mature bud scars from Saccharomyces cerevisiae isolated by both chemical and enzymic treatment of cell walls were observed by selected-area electron diffraction (SAED), X-ray diffraction and electron microscopy with simultaneous physico-chemical characterization (including molar mass, intrinsic viscosity and crystallite size) of α-chitin and glucan. The SR, composed of glucan with strong 0.608; 0.397 and 0.293 nm X-ray reflections, was formed at the start of budding. The SAED patterns of α-chitin both in the adjacent circular zone and in the parts of newly formed primary septum (PS), observed when the development of the PS started, did not differ from those of α-chitin in the single mature bud scar. The bud scar consisted of α-chitin, glucan and mannan and their content, as well as the crystallite size of chitin, depended on the mode of preparation.

Dilute solution properties of aliphatic polyamides

The development of and new trends in the determination of molecular weights and molecular weight distribution of aliphatic unsubstituted linear polyamides (nylons) are reviewed here. Critically discussed are intrinsic viscosity — molecular weight relationships and the conformational regidity of nylon chains. Attention is also given to some peculiarities in the behavior of nylons in multicomponent solvents.

Characterization of copolymers by the light scattering method from dilute solutions in mixed solvents

Abstract Conditions have been established suitable for the determination of the molecular characteristics and the parameters of composition heterogeneity for copolymers by the light scattering method in dilute solutions. These conditions are easiest to realize by using mixed solvents. A relationship has been derived describing the intensity of light scattered from the solution of a chemically heterogeneous copolymer in a mixed solvent. The method can also be applied to copolymers of components having equal refractive indices; it has been checked on mixtures of polyethyleneglycol methacrylate, polymethyl methacrylate and their copolymers in the system methylcellosolve-α-bromonaphthalene. Experimental results were in good agreement with the calculated values.

Block copolymer micelles near critical conditions

A three-block copolymer poly(styrene-block-hydrogenated butadiene-block-styrene) forms in 1,4-dioxane and 1,4-dioxane/30 vol% n-heptane mixture spherical micelles with aliphatic cores and polystyrene shells. Properties of these micelles near critical conditions, i.e., above the critical micelle concentration (CMC) and below the critical micelle temperature (CMT) have been studied by light scattering. Integral light scattering is proportional to the weighted contributions of the molar masses of two species present in the solutions under study. Quasielastic light scattering, on the other hand, can provide in principle, the values of diffusion coefficient pertaining predominantly to micelles. Experimental data, namely concentration dependences of the diffusion coefficient and of the apparent mass-average molar mass, strongly deviate from the expected pattern predicted by the model of closed association. The deviation consists in an increase of both molar mass and hydrodynamic radius of micelles in a particular concentration region above CMC.

Dilute solution properties of polylaurolactam

Abstract For a number of fractions and unfractionated samples of polylaurolactam, molecular weights ( M w = 1 × 10 4 −12·5 × 10 4 ) were measured by the light-scattering method in a mixed solvent of m-cresol with 60 vol. % 2,2,3,3-tetrafluoropropanol; intrinsic viscosities were determined in m-cresol and 96% H2SO4, and the constants of the Mark-Houwink equation were calculated. The calculated values of the characteristic ratio of unperturbed dimensions (virtually identical for m-cresol and 96% H2SO4) were compared with the respective values for polypyrrolidone and polycaprolactam. It was found that the higher frequency of the CONH-groups reduces the rigidity of the polyamide chain.